Add logoutLocal() method that only clears local session
and does not logout from the CAS server.

 uphpCAS.php

@@ -122,10 +122,14 @@
            .($returnUrl ? '?service='.urlencode($returnUrl) : '');
    }
    
    public function logout($returnUrl = NULL) {
    public function logoutLocal() {
        @session_start();
        unset($_SESSION[$this->sessionName]);
    }
	
    public function logout($returnUrl = NULL) {
        $this->logoutLocal();
        if($this->isAuthenticated()) {
            unset($_SESSION[$this->sessionName]);
            header('Location: '.$this->logoutUrl($returnUrl));
            die();
        } elseif($returnUrl) {